Water is a tricky substance, which is why diagnosing a leak is often such a hassle. A few entries back, I wrote about locating leaks around your bathroom sink and diagnosing what exactly caused them. What I left out is the all too familiar sign of water damage on the ceiling of the room below your bathroom. Now, sure, most of the time, this is a clear sign that there’s something wrong with your upstairs bathroom or kitchen’s plumbing but this is not 100% true. Indeed, as I mentioned earlier, water knows how to travel, and the water damage could just as well be from piping leading from your attic or roof or other second-story plumbing.
Lets look at showers and baths as an example of pinpoint and differentiating. Leaks from baths and showers are as common as those from faucets or toilets, so its worth knowing how to zero in on the trouble spots. The most common origin spot is the grout around the tiles, which can shrink and allow water in behind the tiles. Other popular spots are the tub’s filler, which may have a worn-out washer or an improperly sealed valve threads, and the tub itself, which might similarly suffer from improper sealing or cracks that are (usually) easily identifiable. Less likely but possible culprits include a problem with the overflow pipe (worn-out or shoddily installed overflow washer) or the drain (clogged outlet pipe).
For the drain, a simple way to test is to run a length of tubing (black rubber will do) from your vanity faucet fixture to your drain and send water down the drain for anywhere from 10-20 minutes. If the leak doesn’t show up, you know the drain and the attached plumbing is secure. And unless the leak is constant throughout the day, the hot and cold water valves are not the culprits.
The next suspects are the tub and the tub filler. The latter is easy enough to check: Just fill your tub and look for a leak from the filler (the tub faucet). This usually denotes broken piping, usually on a copper elbow. As for the tub overflow, close your tub drain and fill the tub to the overflow and look for your leak; if this ends up being your trouble, it likely will require the replacing of the sealing or the washer on your overflow.
The most complex check is the plumbing behind the showerhead. You’ll need to take off the showerhead and cap the stem with a threaded cap before running the water. After 10 to 15 minutes, check the leak area. If this turns out to be the problem, you will need a plumber to look at the rest of the stem and the piping behind and below the showerhead.
The very last check is the most common: The grout. The DIY check requires you to run water over each wall of your shower individually for ten minutes, either using the showerhead or a hose from another water source. A plumber will likely be needed, regardless, but the more information you have to give him makes the job quicker and the price, in most scenarios, at least minutely less expensive.